Way for delete all object inside an Collection "Mycoll" in blender 2.8
Unlink an object to remove it from a collection.

Py console code, for example sake, creates a new collection that is a copy of "Collection 1".  It contains the default file objects "Cube" "Camera" and "Lamp", and like the original is a child of scene collection.

&gt;&gt;&gt; mycol = D.collections['Collection 1'].copy()
&gt;&gt;&gt; mycol.name
'Collection 1.002'

&gt;&gt;&gt; mycol.objects[:]
[bpy.data.objects['Cube'], bpy.data.objects['Lamp'], bpy.data.objects['Camera']]


To get by name and remove the "Cube" object from collection. (If there is no object named "Cube" in collection get returns None)

&gt;&gt;&gt; cube = mycol.objects.get("Cube")
&gt;&gt;&gt; # remove it from collection
&gt;&gt;&gt; mycol.objects.unlink(cube)
&gt;&gt;&gt; mycol.objects[:]
[bpy.data.objects['Lamp'], bpy.data.objects['Camera']]


Loop thru and empty the whole collection.  Note mycol.objects is boolean False when emtpy.

&gt;&gt;&gt; while mycol.objects:
...     mycol.objects.unlink(mycol.objects[0])
...     
&gt;&gt;&gt; mycol.objects[:]
[]


To remove the object ob  from file use bpy.data.objects.remove(ob, do_unlink=True)  Unlinking do_unlink=Trueis the default, and hence can be left out, will unlink from the collection, and all others containing this object, for you.